Khazhismel Kumykov <khazhy@xxxxxxxxxx> writes:
> On Thu, Dec 26, 2019 at 3:48 PM Gabriel Krisman Bertazi
> <krisman@xxxxxxxxxxxxx> wrote:
>>
>> From: Bharath Ravi <rbharath@xxxxxxxxxx>
>>
>> Connection failure processing depends on a daemon being present to (at
>> least) stop the connection and start recovery. This is a problem on a
>> multipath scenario, where if the daemon failed for whatever reason, the
>> SCSI path is never marked as down, multipath won't perform the
>> failover and IO to the device will be forever waiting for that
>> connection to come back.
>>
>> This patch performs the connection failure entirely inside the kernel.
>> This way, the failover can happen and pending IO can continue even if
>> the daemon is dead. Once the daemon comes alive again, it can execute
>> recovery procedures if applicable.
>>
>> Changes since v2:
>> - Don't hold rx_mutex for too long at once
>>
>> Changes since v1:
>> - Remove module parameter.
>> - Always do kernel-side stop work.
>> - Block recovery timeout handler if system is dying.
>> - send a CONN_TERM stop if the system is dying.
>>
>> Cc: Mike Christie <mchristi@xxxxxxxxxx>
>> Cc: Lee Duncan <LDuncan@xxxxxxxx>
>> Cc: Bart Van Assche <bvanassche@xxxxxxx>
>> Co-developed-by: Dave Clausen <dclausen@xxxxxxxxxx>
>> Signed-off-by: Dave Clausen <dclausen@xxxxxxxxxx>
>> Co-developed-by: Nick Black <nlb@xxxxxxxxxx>
>> Signed-off-by: Nick Black <nlb@xxxxxxxxxx>
>> Co-developed-by: Vaibhav Nagarnaik <vnagarnaik@xxxxxxxxxx>
>> Signed-off-by: Vaibhav Nagarnaik <vnagarnaik@xxxxxxxxxx>
>> Co-developed-by: Anatol Pomazau <anatol@xxxxxxxxxx>
>> Signed-off-by: Anatol Pomazau <anatol@xxxxxxxxxx>
>> Co-developed-by: Tahsin Erdogan <tahsin@xxxxxxxxxx>
>> Signed-off-by: Tahsin Erdogan <tahsin@xxxxxxxxxx>
>> Co-developed-by: Frank Mayhar <fmayhar@xxxxxxxxxx>
>> Signed-off-by: Frank Mayhar <fmayhar@xxxxxxxxxx>
>> Co-developed-by: Junho Ryu <jayr@xxxxxxxxxx>
>> Signed-off-by: Junho Ryu <jayr@xxxxxxxxxx>
>> Co-developed-by: Khazhismel Kumykov <khazhy@xxxxxxxxxx>
>> Signed-off-by: Khazhismel Kumykov <khazhy@xxxxxxxxxx>
>> Signed-off-by: Bharath Ravi <rbharath@xxxxxxxxxx>
>> Co-developed-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>
>> Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>
>> ---
>> drivers/scsi/scsi_transport_iscsi.c | 63 +++++++++++++++++++++++++++++
>> include/scsi/scsi_transport_iscsi.h | 1 +
>> 2 files changed, 64 insertions(+)
>>
>> diff --git a/drivers/scsi/scsi_transport_iscsi.c b/drivers/scsi/scsi_transport_iscsi.c
>> index 271afea654e2..c6db6ded60a1 100644
>> --- a/drivers/scsi/scsi_transport_iscsi.c
>> +++ b/drivers/scsi/scsi_transport_iscsi.c
>> @@ -86,6 +86,12 @@ struct iscsi_internal {
>> struct transport_container session_cont;
>> };
>>
>> +/* Worker to perform connection failure on unresponsive connections
>> + * completely in kernel space.
>> + */
>> +static void stop_conn_work_fn(struct work_struct *work);
>> +static DECLARE_WORK(stop_conn_work, stop_conn_work_fn);
>> +
>> static atomic_t iscsi_session_nr; /* sysfs session id for next new session */
>> static struct workqueue_struct *iscsi_eh_timer_workq;
>>
>> @@ -1611,6 +1617,7 @@ static DEFINE_MUTEX(rx_queue_mutex);
>> static LIST_HEAD(sesslist);
>> static DEFINE_SPINLOCK(sesslock);
>> static LIST_HEAD(connlist);
>> +static LIST_HEAD(connlist_err);
>> static DEFINE_SPINLOCK(connlock);
>>
>> static uint32_t iscsi_conn_get_sid(struct iscsi_cls_conn *conn)
>> @@ -2247,6 +2254,7 @@ iscsi_create_conn(struct iscsi_cls_session *session, int dd_size, uint32_t cid)
>>
>> mutex_init(&conn->ep_mutex);
>> INIT_LIST_HEAD(&conn->conn_list);
>> + INIT_LIST_HEAD(&conn->conn_list_err);
>> conn->transport = transport;
>> conn->cid = cid;
>>
>> @@ -2293,6 +2301,7 @@ int iscsi_destroy_conn(struct iscsi_cls_conn *conn)
>>
>> spin_lock_irqsave(&connlock, flags);
>> list_del(&conn->conn_list);
>> + list_del(&conn->conn_list_err);
>> spin_unlock_irqrestore(&connlock, flags);
>>
>> transport_unregister_device(&conn->dev);
>> @@ -2407,6 +2416,51 @@ int iscsi_offload_mesg(struct Scsi_Host *shost,
>> }
>> EXPORT_SYMBOL_GPL(iscsi_offload_mesg);
>>
>> +static void stop_conn_work_fn(struct work_struct *work)
>> +{
>> + struct iscsi_cls_conn *conn, *tmp;
>> + unsigned long flags;
>> + LIST_HEAD(recovery_list);
>> +
>> + spin_lock_irqsave(&connlock, flags);
>> + if (list_empty(&connlist_err)) {
>> + spin_unlock_irqrestore(&connlock, flags);
>> + return;
>> + }
>> + list_splice_init(&connlist_err, &recovery_list);
>> + spin_unlock_irqrestore(&connlock, flags);
>> +
>> + list_for_each_entry_safe(conn, tmp, &recovery_list, conn_list_err) {
>> + uint32_t sid = iscsi_conn_get_sid(conn);
>> + struct iscsi_cls_session *session;
>> +
>> + mutex_lock(&rx_queue_mutex);
> This worried me a bit, but it seems we won't destroy_conn while it's
> on the err list - cool.
>> +
>> + session = iscsi_session_lookup(sid);
>> + if (session) {
>> + if (system_state != SYSTEM_RUNNING) {
>> + session->recovery_tmo = 0;
>> + conn->transport->stop_conn(conn,
>> + STOP_CONN_TERM);
>> + } else {
>> + conn->transport->stop_conn(conn,
>> + STOP_CONN_RECOVER);
>> + }
>> + }
>> +
>> + list_del_init(&conn->conn_list_err);
>> +
>> + mutex_unlock(&rx_queue_mutex);
>> +
>> + /* we don't want to hold rx_queue_mutex for too long,
>> + * for instance if many conns failed at the same time,
>> + * since this stall other iscsi maintenance operations.
>> + * Give other users a chance to proceed.
>> + */
>> + cond_resched();
>> + }
>> +}
>> +
>> void iscsi_conn_error_event(struct iscsi_cls_conn *conn, enum iscsi_err error)
>> {
>> struct nlmsghdr *nlh;
>> @@ -2414,6 +2468,12 @@ void iscsi_conn_error_event(struct iscsi_cls_conn *conn, enum iscsi_err error)
>> struct iscsi_uevent *ev;
>> struct iscsi_internal *priv;
>> int len = nlmsg_total_size(sizeof(*ev));
>> + unsigned long flags;
>> +
>> + spin_lock_irqsave(&connlock, flags);
>> + list_add(&conn->conn_list_err, &connlist_err);
>> + spin_unlock_irqrestore(&connlock, flags);
>> + queue_work(system_unbound_wq, &stop_conn_work);
>>
>> priv = iscsi_if_transport_lookup(conn->transport);
>> if (!priv)
>> @@ -2748,6 +2808,9 @@ iscsi_if_destroy_conn(struct iscsi_transport *transport, struct iscsi_uevent *ev
>> if (!conn)
>> return -EINVAL;
>>
>> + if (!list_empty(&conn->conn_list_err))
> Does this check need to be under connlock?
My understanding is that it is not necessary, since it is serialized
against the conn removal itself, through the rx_mutex, it seemed safe to
do the verification lockless.
It can only race with the insertion, in which case, it will be safely
removed from the dispatch list here, under rx_mutex, and the worker will
detect and skipped it.
--
Gabriel Krisman Bertazi
